In a nonaqueous electrolyte battery typified by a lithium ion secondary battery, moisture is a factor that deteriorates the cycle characteristics. In view of this, conventionally, mixing a moisture capture agent in an electrode active material layer has been suggested. JP-A-11-260416 (Patent Literature 1) has disclosed the lithium ion battery in which zeolite with the moisture absorption property is mixed in an electrode active material layer.
In the technique disclosed in JP-A-2000-077097 (Patent Literature 2), lithium manganate with high safety as a main positive electrode active material has lithium nickelate mixed therein as another positive electrode active material. This causes lithium nickelate to operate as a hydrogen ion capture agent, thereby suppressing the elution of manganese.
An electrode of a nonaqueous electrolyte battery is formed so that a number of active material particles generally having electric conductivity are bound with each other through a binder. At the same time as intercalating or deintercalating ions, the active material particles generate charges. The charges are transferred between the active material particle and the current collector through a contact point between the active material particles.
Incidentally, in the battery with the structure according to Patent Literature 1, zeolite is taken as the solid insulating particle in the electrode active material layer. Therefore, zeolite cannot carry charges even when zeolite is in contact with the active material particle. For this reason, zeolite has interrupted the current flow. Patent Literature 1 also describes that zeolite is set outside the electrode and inside the battery case. In this case, zeolite does not adversely affect the charge transfer in the electrode. However, zeolite is set at the place away from the place where the presence of moisture leads to a problem, i.e., where the electrochemical reaction occurs. Thus, the effective water absorption by zeolite has not been realized.
From another perspective, it has also been known that the active material layer is formed to include a plurality of kinds of mixed active material particles with different characteristics and this active material layer is used in the electrode as disclosed in Patent Literature 2. In Patent Literature 2, however, in the mixed electrode including the mixed plural kinds of active material particles, one active material particle with high resistance against moisture in the air may be combined with another active material particle that easily reacts with moisture in the air. For example, lithium nickelate easily causes the reaction that generates impurities such as lithium hydroxide by the action of the moisture in the air as compared to other active materials such as lithium oxide. Thus, lithium nickelate easily causes deterioration. Moreover, the impurities generated by the deterioration have resulted in the lower battery cycle characteristics.
In this regard, for example, examination has not been sufficiently conducted on the use of a moisture capture agent as the moisture countermeasure for improving the storability of the electrode in the system employing a mixed electrode including the active material with low resistance against the moisture such as lithium nickelate and another active material that have been mixed.